Wideband Code Division Multiple Access (WCDMA) radio access technology based on 3rd Generation Partnership Project (3GPP) mobile communication system has evolved worldwide. High Speed Downlink Packet Access (HSDPA) that can be defined as the first evolution stage of the WCDMA provides the 3GPP with radio access technology having competitiveness in the mid-term future. However, as the requirements and expectations of users and business providers continuously increase and competitive radio access technology developments are in progress, a new technology evolution in the 3GPP is required for the future competitiveness.
One of systems that are taken into consideration in the post third generation system is an orthogonal frequency division multiplexing (OFDM) system that is able to mitigate inter-symbol interference (ISI) with low complexity. The OFDM system is adapted to transform serial input data symbols into N parallel data symbols and transmit the data symbols with N subcarriers. The subcarriers maintain its orthogonality in the frequency domain. Each orthogonal subcarrier undergoes independent frequency selective fading and the ISI can be canceled through cyclic prefix. Orthogonal frequency division multiple access (OFDMA) refers to realize multiple access by independently providing each user with some of available subcarriers in a system using the OFDM as a modulation scheme. In general, the OFDMA system is adapted to provide frequency resources, called subcarriers, to respective users and provide respective frequency resources to a plurality of users independently so that they are not overlapped with one another. Consequently, the frequency resources are allocated to respective users exclusively.
One or more cells are generally disposed in one base station (BS). A plurality of user equipments (UEs) can be placed in one cell. In general, a UE transmits a radio resource control (RRC) connection request message to the BS in order to gain access to the BS and the BS transmits a RRC connection setup message through a shared data channel. Before establishing the RRC connection, the UE cannot receive any dedicated RRC message. The UE can acquire the RRC connection setup message over a shared data channel by monitoring a shared control channel corresponding to the shared data channel. However, a problem arises because the UE cannot decide which shared control channel is monitored.